Air conditioning system



July 21, 19 2- R. B. P. CRAWFORD AIR CONDITIONING SYSTEM Filed April20', 1959 5 Sheets-Sheet l Roberl 5.?- Crawford.

, R. B. P. CRAWFORD 2,290,465

AIR CONDITIONING SYSTEM.

Filed April 20, 1939' 5 Sheets-Sheet 2 Jul 21, 1942.

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"attorney July 21, 1942- R. B. P. CRAWFORD AIR CONDITIONING SYSTEM FiledApril 20, 1959 5 Sheets-Sheet 4 ilnbentor Roberi B.P. Crawford m ma" mwrwhr

Gttorneg y R. B.VP. CRAWFORD 2,290,465

A IR CONDITIONING SYSTEM Filed April 20, 1939 5 Sheets-Sheet 5 jihlmrdorKobeii 3.2 Crawford. V

Patented duly 21, 1942 AIR conm'rromo SYSTEM Robert B. r. Crawford,Miami, Fla. ApplicationApril 20, 1939, Serial No.268,929

20 Claims.

This invention relates to air conditioning systems.

An object of this'invention is to provide an improved automaticallycontrolled air conditioning system for an enclosure which will act todehumidify and cool, dehumidify and heat, ventilate, heat, and heat andhumidity as required whereby desiredtemperature andhumidity conditionsare at all times automatically maintained within the enclosure.

Another object of this invention is to provide the air conditioningsystem with a chemical dehumidifying arrangement which under certainconditions may automatically be made to heat as well as dehumidifywithout the use of external heat, this being accomplished by thev use oflatent heat of dehumidification.

Still another object of this invention is to provide a two-stagechemical dehumidifying arrangement and an evaporator-absorberarrangement for supplying chilled water for cooling purposes whereinrelatively cool solution is taken from the second stage of thedehumidiiying unit and delivered to the evaporator-absorber and whereinrelatively warm solution is taken from the evaporator-absorberarrangement and delivered to the first stage of the dehumidifying unit.

A further object of this invention is to utilize a vacuum pump inconnection with an evaporator-absorber cooling arrangement to reduce thefriction of air therein and controlling the vacuum pump to control thecooling capacity of the evaporator-absorber cooling arrangement.

Another object is to provide an air conditioning system wherein only thefresh air is dehumidified and controlling the amount of dehumidifiedfresh air andreturn air utilized in accordance with enclosure relativehumidity conditions to maintain desired relative humidity conditions inthe enclosure.

The combination of the various units of the air conditioning apparatusinto a complete air conthe automatic controls applied thereto,

Figures 2, 3, and 4 illustrate diagrammatically the structure andsequence of operation of the automatic controls utilized in Figure 1.

Figures 5 and 6 diagrammatically illustrate various manners in which theconcentration of the hygroscopic fluid may be controlled.

Referring now to Figure 1, an enclosure in the form or a space orbuilding, the temperature and relative humidity of which is to becontrolled, is designated at III. The air within the space lu isconditioned by an air conditioning unit generally designated at II. Thisair condition ing unit ll may be provided with a fresh air inlet duct lzwhich in turn may be provided with iresh air dampers l3 and a filter Il. The fresh air drawn through the fresh air inlet l2 passes through aunit which dehumidifies or humidifies the fresh air and is shown tocomprise a spray l5, cooling coils l6 and ",and a spray it. Asump l9provided with a bafiie or weir 2!! is utilized for collectinghygroscopic fluid, such as calcium chloride, lithium chloride, zincchloride, etc., emanating from the sprays l5 and I8. This unit,

, which Will be termed herein as a dehumidifying unit, is utilized forthe purpose of reducing the saline solution or other hygroscopic fluidcirculating out of sprays l5 and I8 in sequence is below the vaporpressure of the' air passing these points resulting in a condensation ofmoisture and an approach toward equalization of the vapor pressures. Thevapor pressure of the hygroscopic fluid passing out of the sprays l5 andI8, respectively, and over coils I6 and i1 is controlled by theconcentration and temperature of the solution at these points. Thecooling coils l6 and I! are kept at the proper temperature by means of asource of cooling fluid to cool the hygroscopic fluid fordehumidification purposes.

A return air duct 23 provided with a damper 24 operated by aproportioning motor 25 supplies return air from the space or buildingill to the air conditioning unit II. The return air and the fresh airare mixed and passed through temperature changing coils26 which operateto cool or heat the air. A fan 21 operated by -a motor 28 draws the airthrough the air conditioning unit II and discharges the air at desiredtemperature and relative humidity conditions through a discharge duct 29to the space or building III. 1

Cooling fluid for the coils l6 and I! in the de "l6 and H at desiredvalues.

humidifying unit may be provided by means of a cooling tower generallydesignated at 30. This cooling tower 30 may comprise a casing 3|provided with an air inlet 32 and an air outlet 33. A fan 34 driven byan electric motor 35 circulates air through the inlet 32, the chamber3|, and the outlet 33. A spray 36 sprays water to be cooled into thechamber 3| and the water so sprayed contacts the air passing through thechamber 3| and is cooled by evaporation. An electrically operated pump31 withdraws water from the coil l6 through pipe 38 and discharges thiswater through pipe 39 and spray36 into the chamber 3|. The water cooledby-evaporation is collected in the lower part of the chamber 3| andpasses through a pipe 40 into the coil l1. The coils H and I6 areconnected together by a pipe 4| to provide a complete cool watercirculating system. Accordingly cool water is supplied from the coolingtower 30 through the coils |1 and i6 and is returned by the pump 31 tothe cooling tower to be cooled. 'It is here noted that the coils I1 andI6 are arranged in counter-flow relation with the fresh air so that themaximum amount of cooling is obtained. A valve 42 operated by a float 43supplies makeup-water through a pipe 44 from any suitable source ofwater (not shown) to the cooling tower 30 to make up the water lost byevaporation therein. A valve 45 operated by an electric motor 46 may beutilized to close off the supply of-makeup water to the cooling tower 30when it is desired to shutdown this portion of the system. A valve 41may be located in the pipe 40 leading from the cooling tower 30 to thecooling coil H to control the rate of flow of cool water from the towerto the coil N. This valve may be thermostatically operated by means of amotor 48 connected by a capillary tube 49 to a bulb 50 containing avolatile fluid and located in heat exchange relation with the pipe 38.As the temperature of the water in the pipe 38 increases the valve 41 ismoved toward the open position to increase the rate of flow of coolingfluid to the coils H3 and I1. Likewise as the temperature decreasesindicating that the load is relatively light the valve 41 is movedtowards a closed position to decrease the .rate of flow of cooling fluidto the coils l6 and I1. Accordingly the thermostatically controlledvalve 41 operates to control this portion of the system in the mosteconomical manner and to maintain the temperature of the coils A valve5| operated by an electric motor 52 is utilized for draining thewaterfrom the cooling tower 30 and coils l6 and [1 through a drain 53.When the valve 5| is opened, the valve 45 in the make up water supplyline is closed and all the water in the cooling tower system drains outthrough the drain 53.

This prevents freezing up of this portion of the.

system in the winter-time.

For cooling purposes the coils 26 are supplied with chilled water forcooling the mixture of fresh air and the return air before it isdelivered to the space or building l0. The water supplied to the coils26 is chilled by an evaporator-absorber arrangement generally designatedat 54. This evaporator-absorber arrangement 55 may comprise a vacuumabsorber including a chamber 55 and an evaporator including a chamber56, the two chambers 55 and 56 being connected together by a passage 51.passes from the sump I9 of the dehumidifier unit through a pipe 58 andis sprayed by a nozzle 59 into the vacuum absorber chamber 55. A pumpThe hygroscopic fluid 60 withdraws the hygroscopic fluid from the bottomof the chamber 55 through a pipe 6| and discharges this hygroscopicfluid through a pipe 62, a valve 63, and a pipe 64'to the spray l5. Thehygroscopic. fluid from the spray I5 is collected in the sump IS on theleft-hand side of the weir 20 and is then withdrawn from the sump bymeans of a pump 65 through pipe 66 and is supplied to spray I8 through apipe 61.. The hygroscopic fluid from the spray |8 is collected in thesump on the right-hand side of the weir 20. Accordingly a completecirculating system for the hygroscopic fluid is provided for supplyingthe sprays'l5 and I8 with hygroscopic fluid to dehumidify the airentering the fresh air inlet l2 and for supplying hygroscopic fluid tothe evaporator-absorber arrangement 54 for cooling the water passingthrough the cooling coils 26. The

sump on the right hand side of the weir 20 so that relatively coolhygroscopic fluid is supplied to the evaporator-absorber arrangement 54.

- Some of the hygroscopic fluid flowing from the vacuum absorber chamber55 passes through a valve 68 and a pipe 69 to a concentrator, thestructure and operation of which will be pointed out more fullyhereafter. Preferably the valves 68 and 63 are so adjusted that aboutflve-sixths of the hygroscopic fluid delivered by the pump 60 passesthrough valve 63 to spray l5 and about one-sixth passes through valve 68to the concentrator. Concentrated hygroscopic fluid is supplied from theconcentrator through pipe 10 by a pump 1| to the sump I3 of thedehumidifier unit. By reason of this supplying of concentratedhygroscopic fluid to the dehumidifier unit, the concentration of thehygroscopic fluid delivered by the sprays I6 and I1 is maintained at thedesired value to perform the correct amount of dehumidification.

A heat exchanger 200 may be located in the of the pump 31 through pipes20| and 202 under the control of a valve 203- operated by an electricproportioning motor 204. The motor 204 is controlled by a temperatureresponsive controller 205 connected by a capillary tube 206 to a bulb201 containing a volatile fluid and responsive to the temperature of thehygroscopic fluid leaving the heat exchanger 200. Upon an increase intemperature the-valve 203 is moved towards a closed position to causemore of the cool water leaving the pump 31 to flow through the heatexchanger 200 for cooling the hygroscopic fluid. In this manner thevalve 203 is operated to maintain the temperature of the concentratedhygroscopic fluid delivered to the sump l9 at desired values.

A three-way valve 209 located in the pipe 10 between the heat exchanger200 and the sump l9 and operated by an electric proportioning motor ,2|0may be utilized to by-pass some of the concentrated hygroscopic fluidthrough a pipe 2 directly to the nozzle 59 of the vacuum absorberchamber 55 to increase the cooling action thereof during peak sensiblecooling load periods. The proportioning motor 2|0 and hence the valve209 may be controlled by a temperature responsive controller 2'|2connected by a capillary tube 2|3 to a bulb 2|4 containing ayolatilefluid and responsive to the temperature of the hygroscopic solutionleaving the vacuum absorber chamber 55 through pipe 6|. With a constantflow of hygroscopic fluid through the nozzle 59, a rise in tem-'-absorber chamber 55 varies with the sensible cooling load, thethree-way valve 209 is positioned in accordance with changes in thesensible cooling load.

Water flows from the temperature changing coils 26 through pipes I3 and14 under the controlof a valve I5 operated by a motor I6 to a nozzle 11located inthe evaporator chamber 56.

When the valve I5 is open, water is sprayed into the evaporator chamber56. As pointed out chamber 56 by nozzle TI, some of the water,

sprayed into the evaporator chamber 56 evaporates'and cools theremainder of the water therein to the desired degree. In other words,some of the water emanating from nozzle TI is evaporated to cool theremainder of the water, this evaporation being caused by the absorptionof I water vapor by the hygroscopic fluid of lower vapor pressurespraying from nozzle 59 into the vacuum absorber chamber 55. In order toreduce air friction in the movement of the water vapor molecules fromthe chamber 56 to the chamber-55 a vacuum is produced in the e vapo-'rator-absorber arrangement 54 by means of an electrically operatedvacuum pump 92 which is connected to the chamber 56 by a pipe 93. Thevacuum pump 92 draws air out of the evaporatorabsorber arrangement anddischarges this air against atmospheric pressure on the discharge sideof the pump. While the maximum capacity of the evaporator-absorber.arrangement is reached when the absolute pressure in the chambers 55 and56 is equal to or slightly below the vapor pressure of the hygroscopicsolution delivered at the nozzle 59 which is normally about sixmillimeters of mercury, the evaporation will continue at any pressure ata more reduced capacity for higher absolute pressures. Accordingly bycontrolling the operation of the vacuum pump 92 the cooling capacity ofthe evaporatorabsorber arrangement 54 may be varied. A check valve 94located in the pipe 93 between the chamber 56 and the pump 92 isutilized for preventing the back flow of air into the chamber 56 whenthe vacuum pump 92 is not operating.

Chilled water is collected at the bottom of the evaporator chamber 56and is withdrawn by an electrically operated pump I8 through a pipe I9and is discharged through a pipe 80, valve 8| controlled by an electricproportioning motor 82, pipe 83, manually operated valve 84, and pipes85 and 86 to the temperature changing coils 26. Accordingly a completecirculating system for the water flowing through the temperaturechanging coils 26, is obtained provided the valves 8|, 84, and "I5 areopened. Make up water for this cooling system is supplied to theevaporator chamber 56 through a nozzle 81 from a source of water 88under the contor 90. Accordingly when the valve 69 is opened,

make up water is supplied to this portion of the system. Preferably thetwo nozzles 11 and 81 are so arranged that the upper nozzle dischargesthe warmer water so'as to get theadvantage of the biggest differentialin vapor pressure betweenthese water sprays and the hygroscopic solutionspray emanating from nozzle 59. For ex ample if the make up water isusually warmer than the return water, nozzle 81 would be located abovenozzle 'I'I, as shown. If, however, the temperature of the make up wateris lower than that of the return water, the nozzle 81 is located belowthe nozzle 11. When it is desired to drain this portion of the system avalve 96 operated by a motor 91 may be opened to'drain the Water througha drain 98. When valve 96 is opened for draining purposes, make up watervalve 89 is closed to prevent the supply of make up water to theevaporator chamber 56.

A concentrator for concentrating the hygroscopic solution supplied tothe dehumidifier unit is generally designated at I00 and thisconcentrator may comprise a casing IOI provided with an air inlet I02and an air outlet I03. A fan I04 operated by an electric motor I05circulates air through the inlet I02, the chamber IM and the outlet I03.The airinlet is controlled by a damper I06 operated by an electric motorI6! and the air outlet I03 is controlled by a damper I08 operated by anelectric motor I09. A spray IIO located in the-chamber IOI sprays therelatively weak hygroscopic fluid over a heating coil III which drivesoff the moisture from the hygroscopic solution thereby concentrating thesame.

groscopic fluid is collected in the bottom of chamber IOI. If desiredsuitablecontacting arrangements such as carbon rings, etc., may be 10- Aheat exchanger for causing heat exchange between the warm concentratedhygroscopic fluid flowing from the concentrator I00 and the cool dilutehygroscopic fluid flowing from the evaporator-absorber arrangement 54 isdesignated at trol of a valve 89 operated by an electric mo- I22. Thedilute solution passes through the pipe 69, heat exchanger I22, pipeI23, three-way valve I24 operated by an electric proportioning motor I25and pipe I26 to the spray H0.- Concentrated solution flows from thechamber IOI through pipe I21, three-way valve I28 operated by anelectricprcportioning motor I29, pipe I30, heat exchanger I22, and pipeI0 to the dehumidifying unit-and this concentrated solution may becirculated by a pump II. By causing heat exchange between the two fluidsin the heat exchanger I22, economy of operation is greatly'increased andthe hot concentrated solution is pre cooled. Under certain conditions,as in the winter-time, it isnot desirable to have this heat exchangerelation and therefore pipes I3I and I32 connected aroundthe heatexchanger I22 to the three-way valves I24 andI29, respective- Themoisture is carried out of the cham-, ber IN by the fan I04. Theconcentrated hy- A pipe II3 leads to a source of ly,' are utilized. Thepurpose of this will be pointed out more fully hereafter.

At certain times, as in the winter-time, it is desirable that the coils26 in the air conditioning unit II perform a heating function instead ofa cooling function and to accomplish this steam is supplied to the coils26 from the steam pipe II3 through pipe I35, valve I36 operated by anelectric proportioning motor I3I, manual -valve I38, and pipe 86.Condensate is withdrawn from the coils 26 through valve I39 operated byan electric motor I48 and trap I4I to the condensate line II9.Accordingly when the valves I36, I38, and I39 are opened steam issupplied to the coils 26 for heating purposes. At this time valves I5and 8| are closed so that cooling fluid cannot be simultaneouslysupplied. The manual valves 84 and I38 are not necessary but they may beutilized to prevent absolutely the supply water 44 and controlled by avalve I46 operated by an electric motor I" supplies water to the spraysI5 and I8 to make up for the water given off thereby to the air passingthrough the fresh air inlet I2 in the winter.

Thermostat I58 responds to the dry bulb temperature of the space orbuilding I8 and for purposes of illustration it is assumed that thisthermostat controls between 70 and 80. The thermostat I58 controls theoperation of a proportioning motor I5I which in turn operates a stepcontroller I52. A dew-point controller I53 responsive to the dew-pointtemperature of the air outside of the building positions a proportioningmotor I54 which in turn operates a step controller I55. For purposes ofillustration it is assumed that the dew-point controller I53 controlsbetween outside dew-point temperatures of 80 and 33.

When the outside dew-point temperature is above 35 a relay I65 is pulledin by the step controller I55 and this relay controls the operationofvalves45, 5|, 96 and 88. When the relay is pulled in the valvecontrolling the supply of make up water to the cooling tower 38 isopened so that the float operated valve '42 may maintain the correctamount of water in the cooling tower circuit. In addition when the relayI65 is pulled in the valve 5I which drains the cooling tower circuit andthe valve 96 which drains the chilled water circuit are closed and thevalve 88 which controls the supply of make up water to the chilled watercircuit is under the control of a liquid level controller I69 tomaintain the correct amount of water in the ,chilled water circuit. Whenthe outdoor dewcuit to prevent the further supply of water to these twocircuits. Dropping out of the relay I65 also opens the valves 5I and 96to drain thecooling water out of the cooling water circuit and to drainthe chilled water out of the chilled water circuit. This preventsfreezing up of this portion of the air conditioning system during thewinter-time.

When the outside dew-point temperature is above 35 and the enclosure drybulb temperature is above 74, a relay I66 is pulled in by the stepcontrollers I52 and I55. This relay when pulled in causes operation ofthe cooling tower fan 34 and the cooling water circuit pump 31. Alsowhen this relay is pulled in the valve I5 in the chilled water circuitis open and the valve I39 in the steam circuit is closed. When eitherthe outside dew-point temperature drops below bulb temperature is above74, the step controllers I52 and I55 pull in the relay I64. When therelay I64 is pulled in, the dampers I86 and I88 of the concentrator I88are open and the fan I84 is in operation so that the concentrator I88drives oil moisture from the hygroscopic fluid, the moisture beingcarried out of the concentrator I88 by the fan I84. When either theoutside dew-point temperature falls below 35, or the enclosure dry bulbtemperature falls below 74 providing the outside dew-point temperatureis not above 55, this indicates that cooling or dehumidification is notnecessary. Under these conditions the fan I84 of the concentrator I 88is shut off and the dampers I86 and I88 of the concentrator I88 areclosed whereupon moisture is not taken out of the hygroscopic fluid inthe concentrator I88.

The. valve I46 which controls the supply of make up water to the sump I9is closed when either the outside dew-point temperature is above 55 orthe enclosure temperature is above 74. When both the outside dew-pointtemperature falls below 55 and the enclosure dry bulb temperature fallsbelow 74 the valve I46 is placed under the control of the liquid levelcontroller I61 to maintain the level of the hygroscopic fluid in thesump l9 at a substantially constant value.

' In the summertime when the outside dew-point temperature is above 55and the building temperature is relatively high, say above 74, it isdesirable not only to maintain the relative humidity of the dehumidifiedfresh air at a desired low value but it is also desirable to maintainthis dehumidified fresh air at the lowest possible temperature to affordsome sensible cooling within the building. Accordingly under theseconditions the three-way valves I24 and I28 are positioned by the stepcontrollers I52 and I55 to pass the hygroscopic fluid of relatively highconcentration through the heat exchanger I22 so that the temperature ofthe hygroscopic fluid entering the dehumidifying unit will be relativelylow. If now the outdoor dew-point temperature should be above 55 and itshould be a rainy or damp day whereupon the temperature within thebuilding would tend to decrease, it may be de-: sirable to increase thetemperature of the hygroscopic fluid of relatively high concentrationflowing to the dehumidifying unit so that some heating may be obtainedfrom this relatively creases. It follows then that as the spacetemperature decreases, the temperature of the hygroscopic fluiddelivered to the dehumidifying unit is increased to supply heat to thespace to give-- the occupants of the space a feeling of dry warmth onthese rainy or damp days. When the outside dew point temperaturefalls-below 55 but remains above 35 and the enclosure-dry bulbtemperature is above 74 indicating that cooling" of the enclosure isrequired, the three-way valves I24 and I28 are positioned to cause thehygroscopic fluid of relatively high concentration to flow through theheat exchanger I22 so that the maximum amount of cooling maybe obtained,

by the evaporator absorber arrangement 54. If when the outside dew-pointtemperature is between 55 and 35 and the enclosure dry bulb temperaturefalls below 74 indicating that no sensible cooling is necessary, orifthe outside dew-point temperature should fall below 35 indicating thatno dehumidificationor sensible cooling is required, the heat exchangerI22 is entirely by-passed so that relatively warm hygroscopic fluid isdelivered to the dehumidifying unit for preheating and under certaincircumstances for humidifying the fresh air.

The steam valve I I5 which controls the supply of steam to theconcentrator I controlled by the step controller I52 and the stepcontroller I 55. In addition the steam valve H is also controlled by arelative humidity responsive controller I51 located in the fresh airstream on the discharge side of the dehumidifying 'unit, by atemperature responsive controller I58 connected by a capillary tube I59to a bulb I60 also located in the fresh air stream on the discharge sideof the dehumidifying unit and by a humidity responsive controller 2I6located in the air being discharged from the concentrator I00.

When the outside dew-point temperature is above 55. and the spacetemperature is above 74, the steam valve I I5 is placed under thecontrol of the relative humidity controller I51 to maintain the relativehumidity of the fresh air entering the air conditioning unit between 30%and 35%. Upon an increase in relative humidity of the fresh air enteringthe air conditioning unit the humidity controller I51 moves the valve II5 toward an open position to increase the concentration-of thehygroscopic fluid in the dehumidifying unit to reduce the relativehumidity of the air. Conversely upon a decrease in relative humidity thehumidity controller I 51 moves'the valve II5 towards a closed positionto decrease the concentration of the hygroscopic fluid in thedehumidifying unit to allow the relative humidity to increase,Accordingly, when the outside dew-point temperature is above 55 and thespace dry bulb temperature is above 74 the humidity responsivecontroller I51 operates to maintain the relative humidity of the airleaving the dehumidifying unit between 30% and If now the outsidedew-point temperature is above 55- and the space temperature decreasesbelow 74 which wouldbe caused by a rainy or damp day, the .valve I I5 isplaced under the control of both the relative humidity responsive controller I51vand the temperature responsive con- 'gardless of theincrease in temperature.

fluid delivered to the dehumidifying unit is increased to supply heat tothe space. This therefore causes the temperature of the air passing overthe humidity controller to increase thereby decreasing the relativehumidity of this air. Accordingly it. is desirable to decrease thesetting of the relative humidity controller I51 as the temperature ofthe air increases to maintain the moisture content of the air emanatingfrom the dehumidifying unit substantially constant re- The temperatureresponsive controller under these conditions therefore compensates oradjusts the relative humidity controller I57 to lower'the settingthereof as the temperature increases. For purposes of illustration itisassumed that when the temperature of the air is 70 the relativehumidity is maintained at substantially and as the temperature increasesfrom 70 to 115 the relative humidity of the air is decreased from 30% to15% thereby maintaining the moisture content of the air substantiallyconstant regardless of the temperature of the air. In this manner notonly is the moisture content of the fresh air maintained substantiallyconstant for dehumidification purposes but heat is supplied to the freshair by the dehumidifying unit when needed. When theoutside dew-pointtemperature falls tora value between 55 and and the enclosure dry bulbtemperature is above 74, the steam valve H5 is. placed under the controlof the humidity responsive controller I51 to maintain the relativehumidity of the air entering the air conditioning unit between 30% and35%. In other words,'concentrated hygroscopic fluid is supplied to thesump I 8 of the dehumidifying unit which in turn is delivered to theevaporatorabsorber arrangement 54 for providing sensible cooling. If theoutside dew-point temperature be between 55 and 35?, and the enclosuretemperaturefalls below 74 the steam valve 5 is closed so thatconcentration of the hygroscopic fluid is prevented at this time. Whenthe outside dew-point temperature drops below 35, the steam valve H5 isplaced under the control of the temperature responsive controller I58 tomaintain the temperature of the fresh air entering the air conditioningunit II between 50 and 70 depending upon the heating .load on thesystem. As the temperature of the fresh air leaving the sprays I5 and I8increases the valve H5 is moved towards a closed position to decreasethe temperature of the sprays and as the temperature of the airdecreases the valve H5 is moved towards an open position to increase thetemperature of the sprays. As the temperature of the hygroscopic fluiddecreases, the sprays give up .less moisture to the air and as thetemperature increases the sprays give up more moisture. Accordingly whenthe outside temperature is relatively high, say 40, the tem- 5responsive controller I58 drops so that when the outside temperature isat, say 0, the temperature of the fresh air leaving the sprays ismaintained at substantially 50 with a smaller amount of moisturecontained therein. With such an troller I58. As pointed out above underthese conditions the temperature of the hy p c arrangement as theoutside temperature decreases, the moisture content of the fresh airleaving the sprays decreases to decrease the moisture content of the airin the space III; Frosting of the windows and condensation of moistureon the outside walls of the enclosure is therefore prevented.

Valve 203 which controls the flow of cooling water through the heatexchanger 200 for cooling the hygroscopic fluid of relatively highconcentration in addition to being controlled by the temperatureresponsive controller 205 is controlled by the step controllers I52 andI55. When the outside dew-point temperature is above and the enclosuredry bulb temperature is above the valve 203 is placed under the controlof the temperature responsive controller 205 to maintain the temperatureof the hygroscopic fluid of relatively high concentration between andfor calcium chloride or between and 140 for lithium chloride and zincchloride and similar solutions of low aqueous vapor pressure. scopicfluid increases, the valve 203 is moved towards a closed position tocause more of the cool water to flow through the heat exchanger 200 tocool the hygroscopic fluid and conversely as the temperature of thehygroscopic fluid decreases, the valve 203 is moved towardsan openposition to by-pass more of the cool water around the heat exchanger200.If now'the outside dewpoint temperature falls below 35 or the enclosuredry bulb temperature falls below 75, it is not desirable to precool thehygroscopic fluid since under these conditions this hygroscopic fluid isutilized for heating purposes. Accordingly the step controllers I52 andI55 open the valve 203 to completely by-pass the heat exchanger200'under these conditions.

If during the summertime the sensible cooling load within the enclosureshould become extremely high, say above 80, the step controller I52places the control of the three-way valve 209 under the control of thetemperature responsive controller 2 I2. The temperature responsivecontroller 2I2 graduatingly positions the three-way valve 209 inaccordance with the temperature 01' the hygroscopic fluid leaving theevaporatorabsorber arrangement 54,'this temperature being an indicationof the sensible cooling load within the enclosure I0. As the temperatureof the hygroscopic fluid increases due to an increase the pipe 2| Idirectly to the nozzle 59 in the evaporator-absorber arrangement 54 toincrease the cooling effect thereof. If calcium chloride be used thevalve 209 would start to supply hygroscopic fluid to. the nozzle 59 at92 and would supply the full amount at 102 while for lithium chloridethe valve would be opened gradually As the temperature of the hygrothecooling capacity of the evaporator-absorber arrangement 54. As soon asthe enclosure dry bulb temperature drops below 78 the bulb 92 isshut offto decrease the cooling capacity of the evaporator-absorber arrangement54. In this manner the cooling capacity of the evaporator absorber andhence the temperature within the enclosure is controlled by the stepcontroller I52.

When the outside dew-point temperature is above 35 the step controllerI55 places the control of the chilled water throttling valve 0| underthe control of the step controller I52 operated in accordance withvariations in enclosure dry bulb ations in enclosure dry bulbtemperature when the outside dew-point temperature is above 35".

-When the outside dew-point temperature falls below 35 or the enclosuredry bulb temperature drops below 74 the throttling valve 8| iscompletetly closed and the pump I8 is stopped since as the temperatureincreases from 110 to For zinc chloride the valve would gradually openas the temperature increases from 120 to Any hygroscopic solution chosenwould thus have definite temperature values. Accordingly hygroscopicfluid of relatively high concentration is admitted directly to thenozzle 59 of the evaporator-absorber arrangement in accordance with thesensible cooling load when the dry bulb temperature of the enclosurerises above 80. When the dry bulb temperature within the enclosure isbelow 80 the valve 209 is positioned to cause all of the highlyconcentrated hygroscopic fluid to flow directly to the sump I9.

When the enclosure dry bulb temperature is "above 78, the vacuum pump 92is maintained in 1 operation by the step controller I52 to increase thesystem operates on a heating cycle under these conditions.

The steam valve I36 which controls the supply of steam to the coils 26is controlled by the step controllers I52 and I55 and by a dischargetemierature limit control I" suitably connected by 1. capillary tube toa bulb I12 located in the discharge duct 29. .When the outside dew-pointtemperature is above 55 the step controller I55 maintains the steamvalve I36 closed since no heating is desired at this time by the coils26.

When the outside dew-point temperature falls below 55 the steam valveI36 is placed under the control of the. step controller I52. When thetemperature of the enclosure is above 74 the step controller I52maintains the steam valve I36 closed and when the enclosure temperaturedecreases from 73 to 70 the steam valve I36 is graduatingly positionedtowards an open position to increase the heating efiectof the coils 26.The discharge temperature limit controller I" operates in conjunctionwith the step controller I52 to prevent cold drafts in the enclosure I0when the enclosure temperature is below 74. In this manner desired drybulb temperatures are maintained within the enclosure I0 in thewinter-time.

The return air damper 24 is controlled by a relative humidity responsivecontroller I62 located in the enclosure I0 and by the step controllersI52 and I55. When the outside dewpoint temperature is above 55 andthe'enclosure dry-bulb temperature is above 74, the damper 24 is placedunder the control of the enclosure relative humidity controller I62 tomaintain the relative humidity within the enclosure between 45% and 55%.It the dry bulb temperature within the enclosure should drop below 74the return air damper 24 is closed so that warm, dehumidified fresh airis utilized for .conditioning ,the enclosure. If the outdoor dew-pointtemperature decreases below 55 but remains above 45 the return airdamper 24 is also closed to supoutside dew-point temperature decreasesbelow 45 but remains above 35 the damper 24 is placed under the controlof the relative humidity controller I62 to maintain the relativehumidity outside dew-point temperature is substantially 45 the controlpoint of the relative humidity responsive controller I52 will besubstantially 45% and as the outside dew-point temperature decreases to35 the setting of the relative humidity responsive controller I62 islowered to 35%. Accordingly as the outsidedew-point temperaturedecreases the relative humidity within the enclosure I8 isdecreased toprevent condensation of moisture on the windows and outside walls. Whenthe outside dew-point temperature falls below 35 the return air damper24 is moved to the three-quarter open position so that substantially allreturn air is utilized for conditioning purposes. Under these conditionsonly above 25% fresh air is utilized. Only the return air damper 24 isshown to be automatically controlled since there is sufiicient airresistance in the dehumidifier unit that the fresh air supply will varyinversely with the return air supply.

Obviously the fresh air damper l3 could also be automatically operatedwith the return air:

damper 24 to assure the proper relation between fresh and return air.

While the cooling coils I6 and I1 in the dehumidifier unit I2essentially removed the heat of dehumidification, these cooling coilsneed not necessarily be in the direct path of; the spray of hygroscopicfluid but may be installed downstream beyond the sprays I5 and I8 to actas after-cooling coils. When this type of system is used with solutionsof great hygroscopic power such aalithium bromide and zinc chloride,such adiabatic dehumidification and after-cooling with the samehygroscopic fluid, water and control circuits disclosed herein allowsthe use of less circulating water from the cooling tower 38.

It is obvious that well water or city water may be supplied to thecooling coils l6 and I1 instead of cold water from the cooling tower 30,as'illustrated, and that the concentrator I88 may also be a vacuumevaporator, a sun pan, a direct fired evaporator, or other known meanswithout departing from the spirit of the control system describedherein.

In Figure l, the various controls are shown to be connected to theinstrumentalities controlled thereby by conduits indicated in brokenlines but for a more thorough understanding of the control systemutilized in this invention reference is made to Figures 2, 3, and 4,Figures 3 and 4 being an extension of Figure 2. The space temperatureresponsive controller I50 may comprise-a bellows 220 containing avolatile fluid for operating a lever 22I against the action of anadjustable tension spring 222- The lever 22I operates a slider 223 withrespect to a resistance element 224. Upon a decrease in spacetemperature the slider 223 is moved to the left and upon an increase inspace temperature the slider 223- is moved to the right. For purposes ofillustration it is assumed that the slider 223 assumes theposition shownwhen the space temperature is 80 and the slider 223 movesto the left,upon adecrease space temperature until the space temperature hasdecreased to 70 whereupon the slider 223 assumes an extreme left handposition.

The proportioning motor I5I may be of the type shown and described inPatent No. 2,028,110 granted to D. G. Taylor on January 14, 1936. Powermay be supplied to the proportioning motor I5I by means of wires 226 and221 leading from some source of power (not shown). The proportioningmotor I5I mayalso be provided with control terminals 228, 229, and 238which are connected by wires 23I, 232, and 233, respectively, to thepotentiometer of the space tem-' perature responsive controller I50.

The series connected relay coils (not shown) contained within theproportioning motor I5I are connected (across the control terminals 223and 236, the

junction of these relay coils being connected to the control terminal229. The-proportioning motor I5I operates a shaft 234 forming a part ofthe step controller I52. As will be apparent from the above referred toTaylor patent, with the temperature responsive controller I in theposition shown the proportioning motor I5I is in an extreme position andas the temperature progressively decreases to the proportioning motor isprogressively operated through substantially of rotation. Since such aconstruction is well known in the art a further description is notconsidered necessary.

The shaft 234 which is operated by the proportioning motor I5I and whichforms part of the step controller I52 operates cams 235 through 246,inclusive. Cam 235 operates an arm 248 which in turn operates amercuryswitch 249 having electrodes 258 and'25I. When the temperature withinthe enclosure decreases below 74 the switch 249 is operated to cause themercury,therein to bridge the electrodes 258 and 25I. The cam 236operates an arm 252 which in turn operates a mercury switch 253 havingelectrodes 254 and 255. When the temperature Within the enclosure fallsbelow 74 the switch 253 is tilted to unbridge the electrodes 254 and255. The cam 231 operates an arm 256 which in turn operates a mercuryswitch 251 having electrodes 258 and 255. When the temperature withinthe enclosure falls below .78 the switch 251 is tilted to unbridge theelectrodes 258 and 259. Thecam 238 operates an arm 2 60'which in turnoperates a mercury switch 26I having electrodes 262 and I 263. When thetemperature within the enclosure falls below 74 the switch 26I isoperated to are bridged. The cam 240 operates an arm 218 which in turnoperates a mercury switch 21I having electrodes 212, 213, 214, and 215.When the temperature within the enclosure is above 74 the electrodes 212and 213 are bridged and when the temperaturefalls below 74 theelectrodes 214 and 215 are bridged. The cam 24I operates an arm 216which in turn operates a mercury switch'211 having electrodes 218,219,286, and 28I. Whenthe temperature within the enclosure is abov 74 theelectrodes 218 and 219 are bridged andwhen the temperature falls below74 the electrodes 288 and 23I are bridged.

The cam 242 operates an arm282 which in turn operates a mercury switch,283 having electrodes 284, 285, 286, and 281. When thetemperature withinthe enclosure is above 74 the electrodes 284 and 285 are bridged andwhen the temperature falls below 74 the electrodes 286 and 281 arebridged.

The cam 243 operates an arm 288 which in turn operates a mercury switch289 having electrodes 290, 29I, 292, and 293. /When the temperaturewithin the enclosure is above 14 the electrodes 290 and 29I are bridgedand when the temperature falls below 74 the electrodes 292 and 293 arebridged. The cam 244 operates an arm 294 which in turn operates amercury switch 295 having electrodes 296, 291, 298, and 299. When thetemperature within the enclosure is above 74 the electrodes 298 and 291are bridged and when the temperature falls below 14 the electrodes 298and 299 are bridged. The cam 245 operates an arm 300 which in turnoperates a mercury switch 30I having electrodes 302, 303, 304, and 305.When the temperature within the enclosure is above 00 the electrodes 304and 305 are bridged. The cam 246 operates an'arm 306 which in turnoperates a mercury switch 301 having electrodes 308, 309, 3I0, and 3I I.When the temperature within the .enclosure is above 15 the electrodes308 and 309 are bridged and when the temperature falls below 75 theelectrodes'3l0 and 3 are bridged.

The shaft 234 ofthe step controller operates a slider 3I2 with respectto a. conductor 3I3 and a resistance element 314, the slider 3I2 andresistance element 3 forming a control potentiometer. -As the enclosuredry bulb temperature decreases from 14 to 70 the slider 3I2 isprogressively moved from left to right over the resistance element 3| 4.The shaft 234 of the step controller also operates a slider 3I5 withrespect to a conductor 3I6 and a resistance element 3I1, the slider 3I5and the resistance element 3I1 referred to Taylor patent.

forming a control potentiometer. When the enclosure dry bulb temperaturedecreases from 73 to 70 the slider 3I5 is moved progressively from leftto right across the resistance element 3| 1. The shaft 234 of the stepcontroller also operates a slider 3I8 with respect to a resistanceelement 3I9 and conductors 320 and 32I, the slider 3I8 and resistanceelement 3I9 forming a control potentiometer. When the enclosure dry bulbtemperature decreases from'78" to 15 the slider 3I8 is progressivelymoved from the left to the right of the resistance element M9.

The outdoor dew-point temperature responsive controller I53 may be ofthe type shown and described in Patent No. 2,106,101, granted to Otto A.Labus and Robert B. P. Crawford on January'l8, 1938, and for purposes ofillustration in this application it is shown to comprise acasing 325 inwhich is located a relatively long coil 328 provided with suitable fins.Outside air is drawn over the coil 326 by a fan 321 driven by anelectric motor 328. Water is supplied to the coil 326 from a supply pipe329 under the control of a manually adjustable throttle valve 330 and athermostatic snap action valve 33I. The water. flows through the coil326 and due to'the fins and the relatively long .coil the temperature ofthe water" emanating from the coil 326 through pipe 332 represents theapproxi-.

mate dew-point temperature of the outside air. This water at thedew-point temperature of the outside air then flows into a chamber 333and out through a drain 334. A bellows 335 mounted on the chamber 333 isconnected to a bulb 336 located in the chamber 333. The bulb 336 may beprovided with a volatile fill so that the bellows 335 is expanded andcontracted in accordance with the temperature of the water affecting thebulb 336 and hence, in accordance with the dew-point temperature oftheoutdoor air. The bellows 335 operates a lever 331 against the action ofan adjustable tension spring 338. The lever 331 operates a slider 339across a resistance element 340, the slider 339 and the resistanceelement 340 forming a control potentiometer. When the outside dew-pointtemperature is 80 the slider 339 assumes the position illustrated inFigure 2. As the outside dew-point temperature decreases the slider 339is moved progressively to the left across the resistance element 340until the outside dew-point temperature decreases to 33 whereupon theslider 339 assumes an extreme left hand position. When the temperatureof the water passing to the chamber 33 decreases to 33 a bulb 342located in intimate contact with this water-operates through a capillarytube 3 to close the valve 33I which shuts off the supply of water to thecoil 326. A suitable drain being provided, freezing' up of the coil 326in the winter-time is therefore prevented.

The proportioning motor I54 controlled by the dew-point temperaturecontroller I53 may also be of the type shown and described in the abovePower is supplied to the proportioning motor I54 by means of line wires345 and 349 leading from some source of power (not shown). Theproportioning motor I54 is provided with control terminals 341, 348, and349 which are in turn connected by wires 350, 35I, and 352,respectively, with the control potentiometer of the dew-pointtemperature controller. The proportioning motor operates a shaft 353which forms a part of the step controller I55. The proportioning motorI54 and hence the shaft 353 are positioned in direct accordance with theadjustment of the potentiometer of the dew-point temperature controllerI53. With the slider 339 of the dew-point temperature controller I53 inthe extreme position shown the, proportioning motor I54 is in an extremeposition and as the slider 339 moves progressively toward the left theproportioning motor I54 is moved progressively through substantially ofrotation.

The shaft 353 of the step controller I55 operats cams 355 through 369,inclusive. Cam 355 operates an arm 311 which in turn operates a mercuryswitch 312 having electrodes 313 and 314. When the outside dew-pointtemperature falls below 55 the electrodes 313 and 314 are bridged. Cam356 operates an arm 315 which in turn operates a mercury switch 316having electrodes 311, 318, 319, and 380. When the outside dew-pointtemperature is above 55 the electrodes 311 and 318 are bridged and whenthe outside dew-point temperature falls below 55 the electrodes 319 and380 are bridged. The cam 351 operates an arm 38I which in turn operatesa mercury switch 382 having electrodes 383 and 384. As long as theoutside dew-point temperature is above 35 the electrodes 383 and 384 arebridged.- The cam. 358 operates an arm 385 which in turn operates amercury switch 385 having electrodes 381 and 388 and the electrodes 381and 388 are bridged as long as the outside dew-point temperature isabove 35. The cam 359 operates an arm 389 which in turn operates amercury switch 390 having electrodes 39I and 392 and the electrodes 39Iand 392 are bridged as long as the outside dew-point temperature isabove 35.

The cam 360 operates an am 393 which in 7 turn operates a mercury switch394 having elecswitch 460. When the liquid level of the hygrotrode 395,396, 391, and 398. When the outside dew-point temperature is above 35the electrodes 395 and 396 are bridgedand when the dew-point temperaturefalls below 35 the electrodes 391 and 398 are bridged. The cam 36Ioperates an arm 399 which in turn, operates a mercury switch 400 havingelectrodes 40I, 402,

. 403, and 404. When the outside dew-point temperature is above 45 theelectrodes 4M and 402 are bridged and when the dew-point temperaturefalls below 45. the electrodes 403 and 404 are bridged. The cam 362operates an arm 405 which inturn operates a mercury switch 406 4I5 andM6 are bridged. The cam 364 operates an arm 4" which in turnoperates amercury switch 4I8 having electrodes 4l9, 420, 42I,*

and'422. When the outside dew-point tempera-. ture is above 35electrodes M9 and 420 are bridged and when it falls below' 35 theelectrodes =42I and 422 are bridged. Cam 365 operates an arm 423 whichin turn operates a mercury switch 424 having electrodes 425, 426, 421,and 428. When the outside dew-point temperature is above 55 theelectrodes 425 and 426 are bridged and when the dew-point temperaturefallsbelow 55 the electrodes 421 and 428 are bridged. The cam 366operates an arm 42!! which in turn operates a mercury switch 430 thearrangement being such that when the outside dew-point temperature isabove 35 the elec-- temperature of the enclosure rises above 74 trodes43I and 432 are bridged and when it falls below 35 the electrodes 433and 434 are bridged, The.cam 361 operates an arm 435 which in turnoperates a mercury switch 436 the arrangescopic fluid lowers theelectrodes of the mercury switch 460 are bridged and when the level isrestored 'to the desired value the electrodes of the mercury switch 460are unbridged.- Power is supplied to the electric motor I41 01 the valveI46 by means of line wires 46I and 465 leading from some source of power(not shown). When both the enclosure dry bulb temperature falls below 74and the outside dew-point temperature falls below 55. a circuit iscompleted from the line wire 46I through electrodes 250 and I of themercury switch 249, wire 462', electrodes 313 and 314 of the mercuryswitch 312, wire'463, electric motor I41, wire 464, and mercury switch460 back to the other line wire 465. under these conditions the valveI46 is placed under the control of the mercury switch 460 ofthe liquidlevel controller I61 and is opened and closed by the liquid levelcontroller I61 to maintain the level of the hygroscopic fluid in thesump I9 at a desired value. When either the dry bulb or the outsidedew-point temperature rises above 55 the supply of power to the electricmotor I41 is interrupted and the valve I 46 is closed.

;The relay I64 for controlling the operation of the tan I04, and thedamper motors I01 and I09 for dampers I06 and I06, respectively, maycomprise a relay coil 466 for operating switch arms 469 and 410 withrespect to contacts "I and 412, respectively. When' the relay coil 468is energized the switch arms 469 and 410 are moved into engagement withtheir respective contacts 4, and 412 and when the relay coil 468 isdeenergized the switcharms 469 and "Bare moved out of engagement withtheir contacts 4H and 412 by means of springs, gravity or other means(not shown). Poweris supplied to the relay I64 by means of line wires413-and 414 leading from some source otpower (not shown) When theoutside dew-point temperature is I above'55 a circuit'is completed fromthe line wire 413. through electrodes318 and 311 of the mercury switch316 and relay coil 468back to the other .line wire 414. Accordingly whenthe outside dew-point temperature is above 55 the the outside dew-pointtemperature is above the electrodes 443 and. 444 are bridged and whenthe dew-point temperature falls below 35 electrodes" 445 and 446 arebridged. The-cam, 369:

operates an arm 441 which in turn operates a mercury switch448, thearrangement being such that when .the dew-point temperature-is above 35electrodes 449 and '450 are bridged and when the dew-point temperaturefalls below 35 electrodes I and 452Qare bridged. r

The shaft 353 of the step controller I 'operates a slider 453 withrespect to a conductor 4 54 and a resistance element 455, the slider 453and the resistance element 455 forming a compensah ing potentiometer. Asthe outside'dew-point temperature decreases from 45 to 35 the slider 453is moved progressively to the right across the resistance element 455."a Q The liquid level responsive controller I61 re-=- spending to thelevel of the hygroscopic fluid in the sump-I9 may comprise apivotedlever 458 having ,a float.459 and operating "a mercuryrelay coil 468 isenergized and the relay I64 is pulled in. Movement of the switch arm 410into engagement with, the contact 412 completes a circuit through themotors I01 and I 09 of the;

Hence,

dampers I06 and I08 to open these dampers,

Movement of the switch arm 469 into engagement with the contact41lcompletes a circuit through the electricmotor I05 to cause operation ofthe tan I04. Accordingly when the outside dew-point temperature isabove55 the dampers I06 and I08 are open and the fan '.I'04 is in operaation. when the outside dew-point temperature is between 515and 35 andthe enclosure drybulb temperature is above 74 the relay I64 is alsopulled in 'through'a circuit which may be traced from the line wire413through electrodes 319 and 380 of mercury switch 316,-,electrodes'384and 383 of mercury switch 382, electrodes; .255

and 254 of mercury switch 253, and relay .coil

- 466 back to'the other line wire 414." Accord- 76 in'gly whenthe-outside dew-point temperature is between55? and- 35" andthe'enclosure'drybulb 1 temperature is above ,74'-the -fan I84fis inoperation the ca pers I06 midi-I08 are opened. When either the outsidedewpoint temperature 75.

tails below '35f or the drybulb temperature falls point temperature mentwith its contact. When I are moved out of engagement with The liquidlevel controller I69 responsive to the 'level of the chilled water inthe evaporator-absorber arrangement 54 may comprise a pivoted lever 411carrying a float 418 for operating a mercury switch 419. When the levelof the chilled water lowers the switch 419 is tilted to a position tocause bridging of the electrodes therein and when the level of thechilled water is restored to the desired value the electrodes of themercury switch 419 are unbridged.

The relay I65 for controlling the operation of the valves 45, SI, 96,and 89 may comprise a relay coil 48I for operating switch arms 482, 483,484, and 485 with respect to contacts 486, 481, 488, and 489,respectively. When the relay coil 48I is energized the switch arms 482'and 485 are moved into engagement with their respective contacts 486 and489 and the switch arms 483 and 484 are moved out of engagement withtheir respective contacts 481 and 488. When the relay coil 48I isdeenergized the switch arms 462 and 485 are moved out of engagement withtheir respective contacts. 486 and 489 and the switch arms 483 and 484are moved into engagement with their respective contacts 481 and 488 bymeans of springs, gravity or other means (not shown). Power is suppliedto the relay I65 by means of line wires 490 and 49I leading from somesource of power (not shown) When the outside dew-point temperature isabove 35 a circuit is completed from the line wire 490 throughelectrodes 381 and 388 of mercury switch 386 and the relay coil 48I backto the other line wire 49I to energize the relay coil 48I to pull inthe'relay I65. Upon pulling in of the relay I65 movement of the switcharm 482 into engagement with the contact 486 opens the valve 45 andmovement of the switch arm 485 into engagement with the contact 489places the valve 89 under the control of the liquid level controllerI69. Movement of the switch arms 483 and 484 out of engagement withtheir contacts 481 and 488 upon pulling in of the relay I65 closes thevalves 5| and'96. When the outside dew-point temperature drops below 35'the relay coil 48I is deenergized and the relay- I65 drops out.Dropping out of the relay I65 moves the switch arms 482 and 485 out ofengagement with their respective contacts to close the valves 45 and 89and causes movement of the switch arms 483 and 484 into engagement withtheir'respective contacts to open the valves 5I and 96. Accordingly whenthe outside dewis above 35 the valve 45 is opened, the valve 89 is underthe control of the liquid level controller 169, and the valves 5I and 96are closed. When the outside dew-point temperature falls below 35,valves 45 and 89 are closed and valves 5I and 96 are open.

The relay I66 for controlling the operation of the fan 34, the pump 31,and the valves 15 and I39 may comprise a relay coil 50I for-operatingswitch arms 502, 503, 504, and 505 with respect to contacts 506, 501,506, and 509, respectively. When the relay coil 50I is energized theswitch arms 502, 503, and 504 are moved into engagement with theirrespective contacts and the switch arm 505 is moved out of en agetherelay coil 50I 502, 503, and 504 their respec- 505 is moved isdeenergized the switch arms tive contacts and the switch arm closes thevalve energizes the motor Taylor patent it is seen into engagement withits contact by means of the line wire 5I0 through relay coil 50I,electrodes 39! and 392 of mercury switch 390 and electrodes 262 and 263of ,mercury switch 26I back to the other line wire 5II. Completion ofthis circuit energizes the relay coil 50I and pulls in the relay I66.Pulling in of the relay I66 completes a circuit to the motor 35 of thefan 34 to cause operation of the fan 34, energizes the electricallyoperated pump 31 to cause operation of the same, and energizes the motor16 to open the valve 15. energizes the motor I40 to cause the valve I39to be closed. When either the outside dewpoint temperature falls below35 or the enclosure dry bulb temperature falls below 74 the relay coil50I is deenergized to drop out the relay I66. Dropping out of the relayI66 stops operation of the fan 34 and the pump 31 and 15. Dropping outof the relay Accordingly when both the outside dew-point temperature isabove 35 and the enclosure dry bulb temperature is above 74 the fan 34and pump 31 are operated, the valve 15 is open and the valve I39 isclosed. When either the outside dew-point temperature falls below 35 orthe enclosure dry bulb temperature falls below 74 the fan 34 and thepump 31 are stopped, the valve 15 is closed and the valve I39 is open.

Power is supplied to the vacuum pump 92 from line wires 5I3 and 5I4leading from some source of power (not shown). When the enclosure drybulb temperature is above 78 a'cir- 'cuit is completed from the linewire 5I3 through vacuum pump 92 and electrodes 259 and 258 of switch 251back to the line wire 5 to cause operation of the vacuum pump 92. Whenthe enclosure dry bulb temperature falls below 78 this circuit isinterrupted and the vacuum pump 92 is shut down.

The proportioning motor 25 for operating the return air damper 24 mayalso be of the type shown and described in the above referred to Taylorpatent. Power may be supplied to the proportioning motor 25 by means ofwires 520 and 52I leading from some source of power (not shown). Theproportioning motor 25 may be provided with control terminals 522, 523,and 524. Upon reference to the above referred to that the proportioningmotor 25 may include a pair of series connected coils connected acrossthe terminals 522 and 524, the junction of these coils being connectedto the terminal 523. The proportioning motor 25 also includes abalancing potentiometer connected in parallel with these seriesconnected coils. The proportioning motor 25 is so arranged that when theenergization of the coil connected across the terminals 523 and 524 isless than the energization of the coil connected across the termiv nals523 and '522 the proportioning motor 25 is operated to move the damper24 towards a closed position and when the energization of the coilacross the terminals 522 and 523 is less than the energization of thecoil across the terminals 523 and 524 the proportioning motor 25 Pullingin of the relay I66 de- I40 to open the valve I39.

' is operated to move the dampers 24 towards an and the resistanceelement 534 forming a control potentiometer. Electrically connectedtothe slider 532 and operated in unison therewith is a second slider-535contacting with a center tapped resistance 536. As the relative humid-.ity of the enclosure increases the hygroscopic element 526 expands andthe sliders 529 and 532 move to the right with respect to theirresistance elements and as the relative humidity decreases the sliders529 and 532 move toward the left with respect to their resistanceelements. For purposesof illustration it is assumed that when therelative humidity is at 55% the sliders 529 and 532 are in their extremeright-hand position and as the relative humidity decreases to 35% thesliders move to an extreme left hand position. Accordingly, as therelative humidity decreases from 55% to 45% the slider'529 moves fromright to left across its resistance element '53I and as the relativehumidity decreases from d 45% to 35% slider 532 moves from right to leftacross its resistance element 534.; When the slider 532 is in a midposition with respect to its resistance element 534 the slider 535 is atthe middle of the center tapped resistance 536.

The control terminal 522 of the proportioning motor 25 is connected bywires 538 and 539 to the conductor 530 and henceto the left end of theresistance element 53I. The control terminal 524 is connected by wires540', MI, and 542 to the right end of the resistance element 53 IAccordingly the resistance element 53I is connected across the terminals522 and 524. The

control terminal 522 is also-connected by wires 538 and 54,3, variableresistance 544 and wires 545 and 546 to the left ends of the resistanceelements 534 and 455 and the control terminal 524 is connected by wires540, 54I, 541, and 548 to the right ends of the resistance elements 534and 455. Accordingly the resistance elements 534 and 455 are connectedin parallel with respect to each other and across the control terminals522 and 524. The center tap of the center tapped.

resistance 536 is connectedby wires 549 and 550, variable resistance 55Iand wire 552 to the slider resistance across the terminals 523 and-524is decreased to cause movement of the damper 24 towards a closedposition and as the relative humidity decreases. the external resistanceacross the terminals 522 and 523 is decreased to cause opening movementof the damper 24. Accordingly as the relative humidity in the enclosuredecreases from 55% to 45% the return air damp-- er 24 is moved from aclosed position to an open position and vice versa as the relativehumidity increases from 45% to 55%, the return air damper is moved froman open position towards a closed-position. Since the positioning of thereturn air damper 24 determines the amount of dehumidified fresh airused for controlling the' relative humidity in the enclosure I therelative humidity of the enclosure I0 is maintained within 45% and 55%when the outside'dew- 265, and wires 55'! and 540 back to'the controlpoint temperature is above 55 and the enclosure dry bulb temperature isabove 74.

Assume now that the outside dew-point temperature isv above 55 and thata damp rainy day occurs to cause the 'dry bulb temperature of theenclosure to fall below 74 Under these conditions a circuit is completedfrom the control terminal 523 through wire 554, electrodes 408 and 409of the mercury switch 406, wire 555, electrodes 268 and 269 of themercury switch terminal 524. Completion of this circuit sub---stantially short-circuits the control terminals 523 and 524 to move thereturn air damper 24 to a closed position whereupon substantially alldehumidified fresh air is utilized for conditioning the enclosure I0.Under these rainy day conditions, as pointed out above, the dehumidifying unit acts to supply heat to the dehumidified air so' that desireddry bulb temperatures are maintained within the enclosure.

Assumenow' that the outside dew-point temperature falls below 55 butremains above whereupon a circuit is completed from the .controlterminal 523 through wire 554, elec- 453 so that thelpotentiometersformed .by the slider 532 and variable resistance 534 and the slider 453and variable resistance 455 'form a compensated control system.

Assume now that the outside dew-point temperature is above and the roomdry bulb,

temperature is above 74.a circuit is thereupon completed from the,control terminal 523 through wire 554, electrodes'408 and 401 of themercury switch- 406, wire 555, electrodes 2 61 and 26B of the mercuryswitch 265 and wire 55s to the slider 529 of the'humidity responsivecontroller I62. Accordingly the proportioning the humidity responsivecontroller I62 formed by the slider 529 and the resistance element 53I.As the relative humidity increases the external motor 25-is placed underthe control of the potentiometer of trodes 409 and M0 of the mercuryswitch 406, wire 558, electrodes 402 and 40I .of the mercury switch 400and wires 559, 542, 54I-,.and 5401back to the control terminal 524.Completion of this [circuit substantially short-circuits the controlterminals 523 and 524 to close' the return air damper 24 so thatsubstantially all fresh air is utilized for-conditioning the enclosure,I0.

When the outside dew-point temperature falls below 45 but remains above35 a circuit is completed from the control terminal 523 through wire554, electrodes 409 and M0 of the mercury switch 406, wire 558,electrodes 403 and 404 of the mercury switch 400, wire 560, electrodes396 and 3950f the mercury switch 398 and wire 56I to the sliders 532 and453. Accordingly under these conditions the control potentiometer formedby the slider 532 and resistance.ele-

ment 534 and the compensating potentiometer formed by the slider 453 andthe resistance ele ment 455 are placed in control of the-proportioningmotor 25. Upon an increase in relative humidity the slider 53: moves tothe right to decrease the external resistance across the terminals 523and 524 to operate the proportioning motor 25 in' a direction to closethe. return air damper 24, and upon a. decrease in relative'humidity'the slider 532 is movedto the left' With respect to, theresistance element 534 to decrease the extemal' resistance across theterminals 522 and 523-to cause the .proportionin'g motor 25 to operatein a direction'toopen the return air purpose. The parts are so arrangedthat when the outside dew-point temperature is 45 the control point ofthe relative humidity responsivecontroller I62 will be substantially 45%and as the outside dew-point temperature decreases from 45 to 35 thecontrol point of the relative humidity responsive controller I62 islowered to 35%.. When the outside dew-point temperature is substantially45 the relative humidity responsive controller I62 operates to positionthe damper 24 to maintain the relative humidity of the enclosure atsubstantially 45% and as the outside dew-point temperature decreases to35 the control point of the humidity responsive controller I62 islowered to maintain 35% relative humidity conditions within theenclosure. Summing up, the damper 24 is moved between a closed positionand a three-quarter open position to maintain relative humidityconditions within the enclosure that are adjusted in accordance withvariations in outside dew-point temperature. Hence as the outsidedew-point temperature decreases the relative humidity conditionmaintained within the enclosure also decreases within the aboveprescribed limits.

When the outside dew-point temperature falls below 35 a circuit iscompleted from the control terminal 523 through wire 554, electrodes 409and 4H] of mercury switch 406, wire 558, electrodes 403 and 404 ofmercury switch 400, wire 560, electrodes 391 and 398 of mercury switch394, wire 562, variable resistance 563 and wires 564, 539, and 538 tothe control terminal 522. This circuit substantially short-circuits thecontrol terminals 522 and 523 to cause movement of the damper 25 towardsthe open position, the amount of opening movement being regulated by thevariable resistance 563. Preferably resistance 563 is so adjusted thatthe damper 24 is moved to a three-quarter open position so that when theoutside dew-point temperature is below 35 three-fourths return air andone-fourth fresh air is utilized for conditioning the enclosure II).

The proportioning motor I25 for operating the three-way valve I24 mayalso be of the type shown and described in the above-referred to Taylorpatent. Power is supplied to the proportioning motor I25 by means ofwires 510 and SH leading from some source of power (not shown). Theproportioning motor I25 is pro vided with control terminals 512, 513,and 514. The control terminal 512 is connected by a wire 515 and theconductor 3I3 to the left end of the resistance element 3I4 of the stepcontroller I52. The control terminal 514 is connected by wires 516 and511 to the right end of the resistance element 3I4. Accordingly theresistance element 3 is connected across the control terminals 512 and514.

Assume that the outside dew-point temperature is above 55 andthattheenclosuredry bulb temperature is above 74. A circuit is thereuponcompleted from the control terminal 518 through wire 518, electrodes 4!and M3 of the mercury switch H2 and wires 519 and 580 to the slider 3I2of the step controller I52. Accordingly the control potentiometer formedby the slider 3I2 and the resistance element 3I4 is in control of theproportioning motor I25 and since the slider is in the extreme left handposition the external resistance across the control terminals 512 and513 is substantially short-circuited to position the three-way valve I24to pass the hygroscopic fluid through the heat exchanger I22. Underthese conditions the heat exchanger I22 is in operation to cool thehygroscopic fluid of relatively high concentration flowing to thedehumidifying unit and to heat the hygroscopic fluid of relatively lowconcentration flowing to the concentrator I00.

As the dry bulb temperature of the enclosure decreases from 74 to 70 theexternal resistance across the control terminals 513 and 514 isdecreased to operate the proportioning motor I25 in a direction to movethe valve I24 towards the by-pass position. When the dry bulbtemperature of the enclosure falls to 70 the valve I24 is so positionedthat the heat exchanger I22 is completely by-passed. Accordingly whenthe outside dew-point temperature is above 55 the three-way valve I24 iscontrolled in accordance with variations in enclosure dry bulbtemperature between 74 and 70 to move the valve I24 towards the by-passposition as the temperature decreases.

When the outside dew-point temperature is between 55 and 35 and theenclosure dry bulb temperature is above 74 the control terminal 513 ofthe motor I25 is connected to the slider 3I2 of the step controller I52by means of wire 518, electrodes 5 and 6, of the'mercury switch 4I2,wire 58I, electrodes 42!] and MS of the mercury switch 4I8, wire 582,electrodes 213 and 212 of the mercury switch 21 I, and wires 583 and580. Since the dry bulb temperature within the enclosure is above 74 theslider 3 I2 is engaging the conductor 3I3 so that a substantiallycomplete short-circuit is provided across the terminals 512 and 513 tocause the hygroscopic fluid of relatively highconcentration to passthrough the heat exchanger I22 to be cooled thereby. If now the outsidedew-point temperature be between 55 and 35 and the enclosure dry bulbtemperature should fall below 74 a circuit is completed from the controlterminal 513 of the motor I25 through wire 518, electrodes 5 and 6 ofthe mercury switch 2, wire 58I, electrodes 420 and 8 of the mercuryswitch 4I8, wire 582, electr0des'*'214 and215 of the mercury switch 21 Iand wires 584, 585, and 516 to the controliterminal 514. Completion ofthis circuit substantially completely short-circuits the controlterminals 513 and 514 to operate the valve I24 to a position wherein theheat exchanger I22 is by-passed so that relatively hot hygroscopicfluid-is delivered to the sump I9 for heating purposes. When the outsidedew-point temperature falls below 35 a circuit is completed from thecontrol terminal 513 through wire 518, electrodes H5 and 6 of themercury switch 4I2, wire 58I, electrodes 42I and 422 of the mercuryswitch H8 and wires 586, 585, and 516 to the control terminal 514.Completion of this circuit substantially short-circuits the terminals513 and 514 to operate the threeway valve to cause the hygroscopic fluidto bypass the heat exchanger I22.

Summing up when the outside dew-point temperature is above 55 thethree-way valve I24 is controlled in accordancewith variations in 'drybulb temperature between 74 and 70 to move the valve I24 towards theby-pass position a the temperature decreases. When the outside dew-pointtemperature is between 55 and 35- and the enclosure dry bulb temperatureis 663 through wire 622, electrodes 426 and 425 of Y the mercury switch42 and wires 62:; and an type disclosed in the above referred to Taylorpatent. Power is supplied to this proportioning motor by means of wires59I and 592 leading from some source of power (not shown).

The-

control terminals of the proportioning motor I26 are connected by wires593, 596, and 595 to a potentiometer contained within a housing 536 andoperated by the proportioning motor I25. The potentiometer andconnections are so arranged that the proportioning motor I28 movessimultaneously and coextensively with the proportioning motor I25. Inthis manner the threeway valves I23 and I28 are equally positioned uponchanges in outdoor dew-point temperatures and enclosure dry bulbtemperature;

The proportioning motor I31 for operating the steam valve I36 may alsobe of the type shown and described in the above referred to Taylorpatent. Power is supplied to the proportioning motor I31 by means ofwires 666 and 66I leading y from some source of power (not shown). Proportioning motor I3! is provided with control terminals 662, 603, and603, the series connected relay coils within proportioning motor I 3!being connected to these control terminals.

The discharge temperature limit control l'II may comprise a bellows 666connected to the bulb' I'I2 located in the discharge duct 29. Thebellows 606 operates a lever 65'! against the action of an adjustabletension spring 666. The lever 601 operates a slider 669 with respect toa resistance element 6I6, the slider 663 and the resistance element BIBforming a limit potentiometer.

For purposes of illustration it is assumed that when the dischargetemperature is 65 the slider 609 assumes the position shown and as thedischarge temperature decreases the slider 669 is moved to the rightuntil the discharge temperature assumes a value of 60-whereupon theslider nected by wires 6I5, BIG, and 6H to the right endsof theresistance element 3H and the resistance element 6I6.. Accordingly theresistance element 3I'I is connected across the control terminals 662and 664. The left end of the resistance element BID is connected bywires 6I8 and BIB to the slider 3I5. .A resistance 626 connected. acrosswires 6M and H9 is utilized for the purpose of balancing the efiect ofthe limiting resistance 6"! when the slider 663 isin the extreme lefthand 1 position as shown in Figure 3.

Assume now that the outside dew-point temperature; is above 55. Underthese conditiofis 'a circuit is completed from the control terminal backto the control terminal 662. This circuit substantially short-circuitsthe control terminals 602 and 663 to operate the proportioning motor I37in a direction to close the valve I36. Accordingly when the outsidedew-point temperature is above 55 the valve I36 is closed.

Assume now that the outside dew-point temperature falls below 55 butthat the enclosure dry bulb temperature isabove 74. Under theseconditions a circuit is completed from the control terminal 663 throughwire 622, electrodes 427 and 426 of mercury switch 424, wire 626,electrodes 2T3 and2l8 of mercury switch .271 and wires 625 and 6I2 backto the control terminal 602. This circuit also substantiallyshort-circuits the terminals 662 and 663 tocause the valve I36 to beclosed. Accordingly when-the outside dew-point temperature falls below55 but the enclosure dry bulb temperature remains above 74 the steamvalve I36 is closed.

When the enclosure dry bulb temperature falls below 7 4 and the outsidedew-point temperature is below 55 a circuit is completed from thecontrol terminal 663 through wire 622, electrodes 62! and628 of themercury switch 626, wire 624, electrodes 28!] and ZBI of the mercuryswitch 217 and wire 626 to the slider 609 of the discharge temperaturelimit control I'II. Since the slider 606 is usually in the extreme lefthand position as shown in Figure 3 the control terminal 663 is thereforedirectly connected to the slider 3I5 of the step controller I52 so thatthe potentiometer formed by the slider 3I5 and the resistance element3Il is in direct control of the proportioning motor I37 under theseconditions. As the space temperature decreases from 73 to 70 theexternal resistance across the control terminals 663 and 603 isprogressively decreased to move the valve I36 progressively towards anopen position and when the space temperature falls to 70 the valve I36becomes wide open. Accordingly when the outside dew-point temperature isbelow 55 and the enclosure temperature falls below 74 the valve I36 isgraduatingly positioned in accordance with variations in enclosuretemperature between 73 and 70 to maintain the enclosure temperature atthe desired value. As pointed out above, the resistance-620 is utilizedfor nullifying the efiect of the limit resistance 6 I 0 when the slider669 is in the position shown in Figure 3.

Assumev now that the outside dew-point temperature is below that theenclosure dry bulb temperature'is between 74" and 73 so that the steamvalve I36 is closed,'if the air entering the 669 adds resistanceinseries'with the slider 3I5 to decrease the controlling -efiect of theslider 3I5 and reduces the external resistance across the controlterminals 663 and 604 to move the valve I36 towards the open position.If the discharge temperature should 'fall tothe valve I36 will becomecompletely open. In this manner the discharge temperature limit controlI'II controls the steam valve I36 when the enclosure temperature isbelow 74 to-prevent the discharge temperature from falling below 'a'desired value, 'illustratively i Summing up, when the outside dew-pointtemperature is above 55 the steam valve I36 is closed, when the outsidedew-point temperature falls below 55 and the enclosure dry bulbtemperature is above 74 the steam valve I36 is also closed and when theenclosure dry bulb temperature falls below"74 providing the outsidedew-point temperature is below 55, the steam valve I36 is placed underthe control of the enclosure dry bulb temperature step controller I52and the discharge temperature limit control |1| to maintain desired drybulb temperature conditions within the enclosure I8 and to preventdrafts within the enclosure I8.

The proportioning motor 82 for operating the chilled water throttlingvalve 8| may also be of the type shown and described in the abovereferred to Taylor patent. Power is supplied to the proportioning motor82 by means of wires 638 and 63| leading from some source of power (notshown). The proportioning motor 82 is provided with control terminals632, 633, and 634, the relay coils contained within the proportioningmotor 82 being connected to these control terminals. The controlterminal 632 is connected by wire 635 and conductor 328 to the left endof the resistance element 3I8 and the control terminal 634 is connectedby wires 636 and 631, resistance 638, wire 639, and conductor 32| to theright end of the resistance element 3l8. Accordingly the resistanceelement 3I8 is connected across the control terminals 632 and 634.

Assume now thatthe outside dew-point temperature is above 35 and theenclosure temperature is above '74", a circuit is thereupon completedfrom the control terminal 633 through wire 638, electrodes 432 and 43|of mercury switch 438, wire 648, electrodes 285'and 284 of the mercuryswitch 283 and wire 64I to the slider 3I8. Accordingly when the outsidedew-point temperature is above 35 and the enclosure temperature is above74, the potentiometer formed by the slider 3|8 and the resistanceelement 3I8 is in control of the prpportioning motor 82. As shown theslider 3I8 is in the extreme left hand position and therefore thecontrol terminals 632 and 633 are substantially short-circuited tomaintain the valve 8| in the wide open position.' As the dry bulbtemperature within the enclosure progressively decreases from 78 to theexternal resistance across the control terminals 633 and 634 isprogressively decreased to move the valve 8| from the wide open positionto a minimum position determined by the resistance value of theresistance 638. Accordingly the valve 8| is graduatingly positionedbetween a wide open position and a minimum position in accordance withvariations in enclosure dry bulb temperature between 78 and 75 tomaintain desired dry bulb temperature conditions within the enclosure|8.

, When the outside dew-point temperature is above 35 and the enclosuredry bulb temperature falls below 74 a circuit is completed from thecontrol terminal 633 through wire 638, electrodes 432 and 43I of themercury switch 438, wire 648, electrodes 286 and 281 of the mercuryswitch 283 and wires 642 and 636 to the control terminal 634. Thiscircuit substantially shortcircuits the control terminal 633 and 634 tomove the valve 8| to a closed position to shut off the circulation ofchilled water.

When the outside dew-point temperature falls,

1 below 35 a circuit is completed from the control terminal 633 throughwire 638, electrodes 433 and of the pump 18. When the valve 8| is movedto the minimum position the switch 641 is opened and whenever the valve8| is moved toward the open position from the minimum position, theswitch 641 is closed. When the switch 641 is closed a circuit iscompleted from the line wire 645 through switch 641, wire 648, andcirculating pump 18 back to the other line wire 646. Summing up, whenthe valve 8| is moved to the minimum position or closed, the pump 18 isstopped and whenever the valve 8| is not in the minimum or closedposition the pump 18 is in operation.

The proportioning motor II6 for operating the steam valve I I5 of theconcentrator I88 may also be of the type disclosed in the above referredto Taylor patent. Power is supplied to the proportioning motor II6 bymeans of wires 658 and 65I leading from some source of power (notshown)". The proportioning motor H6 is provided with control terminals652, 653, and 654, the relay coils contained within the proportioningmotor II6 being connected to these control terminals.

The relative humidity responsive controller I51 responding to therelativehumidity of the fresh air leaving the sprays I5 and I8 maycomprise a hygroscopic element 656 for operating a lever 651 against theaction of an adjustable tension spring 658. The lever 651 operates aslider 658 across a resistance element 660 and a conductor 66I and alsooperates a slider 662 across a conductor 663 and a resistance element664. Mechanically and electrically connected to the slider 662 is aslider 665 movable with respect to a center tapped resistance element666. Upon an increase in relative humidity the sliders 658 and 662 aremoved toward the left and upon a decrease in relative humidity thesesliders are moved toward the right. For purposes of illustration it isassumed that when the relative humidity is 35% the sliders 658 and 662are in the extreme left hand positions. As the relative humiditydecreases from 35% to 30% the slider 658 progressively moves from leftto right across the resistance element 668 and when the relativehumidity decreases from 30% to 15% the slider 662 moves progressivelyfrom left to right across the resistance element 664. When the slider662 is midway along the resistance element 664 the slider 665 engagesthe center of the center tapped resistance element 666.

The temperature controller I58 responding to the dry bulb temperature ofthe fresh air leavment 616. When the dry bulb temperature of the airleaving the sprays I5 and I8 is at 50" the sliders 6H and 614 are in theextreme left hand positions. As the dry bulb temperature increases from50 to 70 the slider 61I is moved progressively from left to right overthe resistance element 612 and when the dry bulb temperature increasesfrom 70 to 115 the slider 614 is moved progressively to the right alongthe resistance element 616.

The humidity responsive controller 2I6 responsive to the relativehumidity of the air leaving the concentrator I may comprise a humidityresponsiveelement 68I for operating a lever 682 against the action of anadjustable tension spring 683. The lever 682 operates a mercury switch684 having electrodes 685, 686, 681, and 688.

When the relative humidity of the air leaving the.

concentrator is normal indicating that the hygroscopic fluid in theconcentrator is not too highly concentrated the electrodes 685 and 686are bridged but when the relative humidity of the air falls to a value,say 25%, indicating that the hygroscopic fiu'id in the concentrator I00is becoming too highly concentrated with danger of the samesolidifying'the mercury switch 684 is tilted to bridge the electrodes681 and 688.

The control terminal 652 of the proportioning motor I I6 is connected bywires 689, 660, and 69! moves to the right to decrease the externalresistance across the control terminals 653 and 654 to move the valve IItowards a closed position.

- Accordingly under these conditions the valve II 5 to the left ends ofthe resistance elements 612- ingly the resistance elements 612 and 660are' connectedacross the control terminals 652 and 654. In a like mannerthe control terminal 652 is connected by wires 639, 696, and 601 to theright end of the resistance element 616 and to the left end of theresistance element 664, and the control terminal 654 is connected bywires 692, 663, 698, 699, and 100 to the left end of the resistanceelement 616 and to the right end of the resistance element 664.Accordingly the resistance elements 616 and 664 are connected across thecontrol terminals 652 and 654. The center tapped resistance 665 isconnected by wires I and 102, variable resistance 103 and wire 104 tothe slider 614 whereby the potentiometer formed by the slider 662 andthe resistance element 664 becomes a control potentiometer and thepotentiometer formed by the slider 614 and the resistance element 616becomes a compensating potentiometer for adjusting the control point ofthe control potentiometer. The variable resistance 103 is utilized inthis connection for the purpose of desensitizing the controlling actionof the compensating potentiometer so that the main control is obtainedby the control potentiometer.

Assume now that the outside dew-point temis graduatingly positioned bythe relative humidity responsive controller I51 to maintain the relativehumidity of the air leaving the sprays I5 and I8 between 30% and3 5%.

Assume now that the outside dew-point teinperature is still above 55 andthat a rainy or damp day occurs to cause the enclosure temperature tofall below 74. Underthese conditions a circuit is completed -from thecontrol terminal I 653 through wire 106, electrodes 686 and 685 ofmercury switch 684, wire 101, electrodes 438 and 431 of the mercuryswitch 436, wire 108, electrodes 292 and 293 of the mercury switch 281and 'wire 1 to the sliders 614 and .662 of the temperature responsivecontroller I58 and the humidity responsive controller I51. Under theseconditions the proportioning motor 6 is placed under the control of acompensated control system having a control potentiometer operated inaccordance with relative humidity and a compensating potentiometeroperated in accordance with dry bulb temperature. As the relativehumidity decreases the slider 662 moves to the right -to decrease theexternal resistance across they control terminals 653 and 654 to movethe valve H5 towards a closed position and as the relative humidityincreases the slider 662 moves to the left to decrease the externalresistance across the control terminal 652 and 653 to move the valve II5towards an open position. Accordingly the valve II5 is graduatinglypositioned in accordance with variations in relative humidity asdetected by the humidity responsive controller I51. by the slider 614and the resistance element 616 acts to shift the control point of thecontrol potentiometer. When the dry bulb temperature is substantially 70the control point of the .relative humidity responsive controller ismaintained at substantially 30% and as the dry bulb temperatureincreases from 70 to 115 the control point of the relative humidityresponsive controller is gradually lowered from 30% to as pointed outabove.

perature is above 55, thatthe enclosure dry bulb and H8 to the slider659 of the relative humidity responsive controller I51. Under theseconditions the potentiometer formed by. theslider 659 and the resistanceelement 660, is placed in con trol of the proportioning motor I I6. Uponan in-' crease in relative humidity the slider 659 moves to the left todecrease the external resistance across the control terminals 652 and653 to move the valve I I5 towards an open position and upon When theoutside dew-point temperature is bethe mercury switch 44 I-wire H3,electrodes 291 and 296 of the mercury switch 295 and wires I I4 and 1 I0to the slider 655. Accordingly, the slider 658 on the relative humidityresponsive controller I51 is placed in control of the steam valve H5 to.maintain the relative humidity of the fresh air leaving the sprays l5and I 8'between and a decrease in relative humidity the slider 656,75

When the outside dew-point temperature falls below 55 but remains above35 and the enclosure temperature falls below 74, a circuitis completedfrom the control terminal 653 through wire 106, electrodes 686 and 685,wire .101, electrodes 439 and 440 of the mercury switch 436,

The compensating potentiometer formed

